[PATCH v2 06/16] KVM: PPC: Book3S HV: XIVE: add controls for the EQ configuration

[Cédric Le Goater]

On 3/14/19 3:32 AM, David Gibson wrote:
> On Wed, Mar 13, 2019 at 10:40:19AM +0100, Cédric Le Goater wrote:
>> On 2/26/19 6:24 AM, Paul Mackerras wrote:
>>> On Fri, Feb 22, 2019 at 12:28:30PM +0100, Cédric Le Goater wrote:
>>>> These controls will be used by the H_INT_SET_QUEUE_CONFIG and
>>>> H_INT_GET_QUEUE_CONFIG hcalls from QEMU. They will also be used to
>>>> restore the configuration of the XIVE EQs in the KVM device and to
>>>> capture the internal runtime state of the EQs. Both 'get' and 'set'
>>>> rely on an OPAL call to access from the XIVE interrupt controller the
>>>> EQ toggle bit and EQ index which are updated by the HW when event
>>>> notifications are enqueued in the EQ.
>>>>
>>>> The value of the guest physical address of the event queue is saved in
>>>> the XIVE internal xive_q structure for later use. That is when
>>>> migration needs to mark the EQ pages dirty to capture a consistent
>>>> memory state of the VM.
>>>>
>>>> To be noted that H_INT_SET_QUEUE_CONFIG does not require the extra
>>>> OPAL call setting the EQ toggle bit and EQ index to configure the EQ,
>>>> but restoring the EQ state will.
>>>
>>> [snip]
>>>
>>>> +/* Layout of 64-bit eq attribute */
>>>> +#define KVM_XIVE_EQ_PRIORITY_SHIFT	0
>>>> +#define KVM_XIVE_EQ_PRIORITY_MASK	0x7
>>>> +#define KVM_XIVE_EQ_SERVER_SHIFT	3
>>>> +#define KVM_XIVE_EQ_SERVER_MASK		0xfffffff8ULL
>>>> +
>>>> +/* Layout of 64-bit eq attribute values */
>>>> +struct kvm_ppc_xive_eq {
>>>> +	__u32 flags;
>>>> +	__u32 qsize;
>>>> +	__u64 qpage;
>>>> +	__u32 qtoggle;
>>>> +	__u32 qindex;
>>>> +	__u8  pad[40];
>>>> +};
>>>
>>> This is confusing.  What's the difference between an "eq attribute"
>>> and an "eq attribute value"?  Is the first actually a queue index or
>>> a queue identifier?
>>
>> The "attribute" qualifier comes from the {get,set,has}_addr methods 
>> of the KVM device. But it is not a well chosen name for the group 
>> KVM_DEV_XIVE_GRP_EQ_CONFIG.
>>
>> I should be using "eq identifier" and "eq values" or "eq state". 
> 
> Yeah, that seems clearer.
> 
>>> Also, the kvm_ppc_xive_eq is not 64 bits, so the comment above it is
>>> wrong.  Maybe you meant "64-byte"?
>>
>> That was a bad copy paste. I have padded the structure to twice the size
>> of the XIVE END (the XIVE EQ descriptor in HW) which size is 32 bytes. 
>> I thought that one extra u64 was not enough room for future.
>>
>>>
>>> [snip]
>>>
>>>> +	page = gfn_to_page(kvm, gpa_to_gfn(kvm_eq.qpage));
>>>> +	if (is_error_page(page)) {
>>>> +		pr_warn("Couldn't get guest page for %llx!\n", kvm_eq.qpage);
>>>> +		return -ENOMEM;
>>>> +	}
>>>> +	qaddr = page_to_virt(page) + (kvm_eq.qpage & ~PAGE_MASK);
>>>
>>> Isn't this assuming that we can map the whole queue with a single
>>> gfn_to_page?  That would only be true if kvm_eq.qsize <= PAGE_SHIFT.
>>> What happens if kvm_eq.qsize > PAGE_SHIFT?
>>
>> Ah yes. Theoretically, it should not happen because we only advertise
>> 64K in the DT for the moment. I should at least add a check. So I will 
>> change the helper xive_native_validate_queue_size() to return -EINVAL
>> for other page sizes.
> 
> Ok.
> 
>> Do you think it would be complex to support XIVE EQs using a page larger 
>> than the default one on the guest ?
> 
> Hm.  The queue has to be physically contiguous from the host point of
> view, in order for the XIVE hardware to write to it, doesn't it?  If
> so then supporting queues bigger than the guest page size would be
> very difficult.

The queue is only *one* page.

C.